Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $245.53   7.367%   $263.6182   $263.62   $263.60   $263.60  
  Purchase #2 $47.65   7.134%   $51.0494   $51.05   $51.05   $51.00  
  Purchase #3 $184.75   11.247%   $205.5288   $205.53   $205.55   $205.50  
  Purchase #4 $229.87   9.825%   $252.4547   $252.45   $252.45   $252.50  
  Purchase #5 $45.99   8.146%   $49.7363   $49.74   $49.75   $49.70  
  Purchase #6 $34.50   12.519%   $38.8191   $38.82   $38.80   $38.80  
  Purchase #7 $179.33   7.819%   $193.3518   $193.35   $193.35   $193.40  
  7 purchase totals = $967.62       $1,054.5583   $1,054.56   $1,054.55   $1,054.50